GENETIC TYPE AND THE ENDOCRINES 683 



ditioned reflex in the pre-operative period. Note the frequent, 

 alert head movements, the rapid, slightly irregular breathing 

 hastened by the stimulus, and the movements of the reacting 

 leg before the metronome was sounded. These latter move- 

 ments were also evoked by the sound of the kymograph in 

 the next room. The metronome sound itself evoked the usual 

 brisk defensive leg movements. Figure 2 shows the striking 

 post-operative behavior of this animal. Note the almost total 

 lack of head movement and general body movement, the 

 slower and more regular breathing curve, and the almost 

 complete absence of movements of the reacting leg. Met. 120 

 evoked only a single weak leg movement. The usual quick 

 unconditioned response to the shock was almost suppressed. 

 As the dog became less and less alert following the opera- 

 tion, the latent period of the motor C-R increased propor- 

 tionally. The average latent period was 3 seconds in the 

 pre-operative period and 7 seconds in the post-operative 

 period, an increase of more than 100 per cent. 



The course of the change in the magnitude of the positive 

 response may be seen in text-figure 122. Note the complete 

 temporary disappearance of the C-R following the operation 

 and the subsequent gradual increase in the magnitude toward 

 the normal during the 3 months of thyroid regeneration. The 

 return toward normal is not complete but the enhancement 

 is clearly seen. 



During the height of the deficiency the only change in 

 behavior outside the laboratory was the appearance of signs 

 of muscular lethargy and a certain lack of responsiveness, 

 but the dog was to all appearances normal at the end of the 

 3 months' period. 



Dog 864 $ , bassethound X shepherd F 2 . An experiment 

 similar to the previous one was now carried out with another 

 dog in which the salivary instead of the motor conditioned 

 reflex was employed. The conditioned stimuli were Met. 120 

 (positive) and Met. 42 and Met. 28 (negative), and the 

 animal was trained for 1 year prior to the operation. 



